The present invention relates generally to personnel shelters for use in the event of a nuclear attack and in particular to a device to prevent a blast wave which accompanies a nuclear explosion from entering the personnel shelter through the ventilation system and causing injury to the personnel and damage to equipment within the shelter.
An earth covered personnel shelter constructed with reinforced concrete and having as its principle construction feature a corrugated steel arch will maintain its integrity even if subjected (from a nuclear blast) to a peak over pressure of about six pounds per square inch (864 pounds per square foot).
Because it is anticipated that it may be necessary to remain within such a personnel shelter for an extended period of time, it is, of course, a requirement of such a shelter that it include a ventilation system connecting the underground space with the atmosphere above. The intake section of the ventilation system is necessarily located above ground and is a potential entry point for a blast wave associated with a nuclear explosion. If the blast wave is permitted to enter into the ventilation system beyond the above ground intacke section, it will at the very least destroy the filter system which filters out radioactive particles from the air being drawn into the shelter and could result in injury to persons and damage to instruments within the shelter.
The present invention traps the blast wave within the blast wave chokes which are within the above ground intake and exhaust sections of the ventilation system. This trapping is accomplished by interference patterns set up as the blast wave strikes one concentric element after the other.